Kepler, Making the Impossible Possible, and Life Beyond Earth

NASA is in the business of making the seemingly impossible possible, from landing on the moon to maintaining a laboratory in space, or from seeing into the far reaches of the cosmos to invading Mars with robots and probes. However, within NASA, there can be resistance to straying too far from the certain or comfortable. This is what William Borucki, the principal investigator of the Kepler mission, ran into time and time again.

Those who are familiar with Kepler may know that the mission has been immensely successful in finding planets outside of our solar system. It be surprising, then, that the proposal for what is now considered to be a largely successful mission was rejected four times.

For those who are unfamiliar, Kepler is a space-based telescope designed to detect planets around other stars. Planets tend to orbit stars in a very regularly, like how the Earth orbits around the sun in a roughly circular path every 365.2 days. If a planet moves in front of a star, the planet will block a small fraction of the light. Since planets tend to orbit in a cyclical fashion, this slight dip in brightness occurs regularly. Based on the decrease in brightness of the star, scientists can determine the size of the planet and from observing how often the star dims, they can determine the orbital period of the planet. Not only is Kepler great for finding planets, but these metrics can also be used to estimate how many planets are potentially in a habitable zone—a narrow orbital band where liquid water can exist on a planet. That is, the planet orbits at a large enough distance to its star so that water won’t be evaporated away by the star’s heat but at a close enough distance so that the water on the planet won’t be frozen all of the time.

At first blush, Kepler seems like a straightforward, self contained mission—a laudable project in and of itself. Yet, William Borucki’s vision extends beyond just Kepler. According to Borucki, Kepler is rooted in something more philosophical, “You have got a goal that’s extremely important for mankind to understand his place in the universe. Is there life out there?” Concrete science is needed in order to answer that abstract idea. “To find the answer, the first thing you do is find out if there are planets in the habitable zone,” he says.

But not everyone shared that vision.Some researchers displayed skepticism of the work that preceded and inspired the idea for Kepler—like the ability to detect a star’s dimming because of a passing planet. As Borucki said, Kepler faced many headwinds: “Everyone ‘knew’ it couldn’t be done. Right? All the early work from the 70s, 80s, and early 90s: ‘Couldn’t be done.’”

The proposal for Kepler was rejected four times over eight years (proposals were reviewed every two years). The rejections pointed to different obstacles that were—theoretically—insurmountable, but Borucki and his team in fact surmounted them.

Kepler was first rejected when the proposal reviewers at NASA thought that no suitable detectors existed for this sort of telescope, so the team used lab tests to show the detectors were sensitive enough. Kepler was rejected a second time because the proposal was too expensive. The team then modified the design to make it less expensive for the next proposal. The idea was rejected a third time because no scientific team had demonstrated an ability to collect and analyze that much data—light from tens of thousands of stars simultaneously—automatically, so the team built an observatory to show that this was possible. Finally, Kepler was rejected for the fourth time because proposal reviewers thought that the changes in brightness would be too minute to measure (light differences of 0.01%). Borucki and his team then designed a way to test their detectors with a technique to simulate small light changes. Finally, the proposal was accepted.

But all that work proving the science was sound and demonstrating that the telescope would be technically feasible was just the beginning. Now that the NASA funders agreed building Kepler was possible, it had to actually be made, and second stage funding wasn’t a guarantee. There were also problems obtaining particular radios and problems with the reliability of parts that have to endure the intense shaking of a rocket launch. On top of that, cost overruns and delays (a perennial problem for NASA programs) nearly killed Kepler.

Why did Borucki persist? “Kepler was just obvious to me that it needed to be done,” he says. And because Kepler survived, the telescope has found over 1000 planets around other stars: when this data is extrapolated to the entire Milky Way, our galaxy is thought to host billions of habitable planets.

But this brings up the Fermi paradox: if there is a large potential for extraterrestrial life, why haven’t we heard from other civilizations? As Borucki pondered, “Up to now, the Fermi paradox has been something philosophers can think about. But now that we know there [are] so many planets in the habitable zone of other stars, the Fermi paradox becomes very real. Why haven’t we heard from anyone? Why has SETI [the search for extraterrestrial intelligence] not picked up a signal in the decades it’s looked?” To address those questions, more missions and other telescopes, like the James Webb Space Telescope, will be needed.

For now, Kepler has been and continues to be a symbol of scientific and technological triumph over adversity. Two of Kepler’s four reaction wheels—flywheels that allow the telescope to steadily point in a single direction—failed between 2012 and 2013, causing Kepler to lose its stable view of the stars it had been studying. The Kepler team responded with characteristic adaptability in the face of what could be a crippling challenge: it thought up a new mission that didn’t need a nearly stationary telescope to keep hunting for new planets. Kepler wasn’t stopped before—and it’s certainly not going to stop now.

About The Author

Alex is a postdoctoral researcher working at NASA Ames Research Center. He received his PhD at Northwestern University. His specialty is computational materials science, which sits on the intersection of atomic physics and computer science. Alex has studied materials including nuclear fuels and shape memory alloys and has written on topics such as exoplanets and the science of smell for The Verge. His interests include space, physics, and data science.